feat(config): add deep_research feature flag to gate Sage agent

crates/forge_config/.forge.toml

@@ -28,6 +28,7 @@ tool_timeout_secs = 300
 top_k = 30
 top_p = 0.8
 verify_todos = true
+research_subagent = false
 
 [retry]
 backoff_factor = 2

crates/forge_config/src/config.rs

@@ -281,6 +281,13 @@ pub struct ForgeConfig {
     /// when a task ends and reminds the LLM about them.
     #[serde(default)]
     pub verify_todos: bool,
+
+    /// Whether the deep research agent is available.
+    ///
+    /// When set to `true`, the Sage agent is added to the agent list and
+    /// the `:sage` app command is enabled. Defaults to `false`.
+    #[serde(default)]
+    pub research_subagent: bool,
 }
 
 impl ForgeConfig {

crates/forge_main/src/ui.rs

@@ -2008,7 +2008,11 @@ impl<A: API + ConsoleWriter + 'static, F: Fn(ForgeConfig) -> A + Send + Sync> UI
                 self.on_agent_change(AgentId::MUSE).await?;
             }
             AppCommand::Sage => {
-                self.on_agent_change(AgentId::SAGE).await?;
+                if !self.config.research_subagent {
+                    self.writeln("Sage agent is disabled. Set `research_subagent = true` in .forge.toml to enable it.")?;
+                } else {
+                    self.on_agent_change(AgentId::SAGE).await?;
+                }
             }
             AppCommand::Help => {
                 let info = Info::from(self.command.as_ref());

crates/forge_repo/src/agent.rs

@@ -162,16 +162,17 @@ impl<F: FileInfoInfra + EnvironmentInfra<Config = ForgeConfig> + DirectoryReader
     AgentRepository for ForgeAgentRepository<F>
 {
     async fn get_agents(&self) -> anyhow::Result<Vec<forge_domain::Agent>> {
+        let config = self.infra.get_config()?;
         let agent_defs = self.load_agents().await?;
 
-        let session = self
-            .infra
-            .get_config()?
+        let session = config
             .session
+            .clone()
             .ok_or(forge_domain::Error::NoDefaultSession)?;
 
         Ok(agent_defs
             .into_iter()
+            .filter(|def| filter_agent(def, &config))
             .map(|def| {
                 def.into_agent(
                     ProviderId::from(session.provider_id.clone()),
@@ -182,9 +183,11 @@ impl<F: FileInfoInfra + EnvironmentInfra<Config = ForgeConfig> + DirectoryReader
     }
 
     async fn get_agent_infos(&self) -> anyhow::Result<Vec<forge_domain::AgentInfo>> {
+        let config = self.infra.get_config()?;
         let agent_defs = self.load_agents().await?;
         Ok(agent_defs
             .into_iter()
+            .filter(|def| filter_agent(def, &config))
             .map(|def| forge_domain::AgentInfo {
                 id: def.id,
                 title: def.title,
@@ -194,6 +197,15 @@ impl<F: FileInfoInfra + EnvironmentInfra<Config = ForgeConfig> + DirectoryReader
     }
 }
 
+/// Returns `false` for agents that are disabled by a feature flag in the
+/// configuration, `true` for all others.
+fn filter_agent(def: &AgentDefinition, config: &ForgeConfig) -> bool {
+    if def.id.as_str() == forge_domain::AgentId::SAGE.as_str() && !config.research_subagent {
+        return false;
+    }
+    true
+}
+
 #[cfg(test)]
 mod tests {
     use pretty_assertions::assert_eq;

forge.schema.json

@@ -241,6 +241,11 @@
         }
       ]
     },
+    "research_subagent": {
+      "description": "Whether the deep research agent is available.\n\nWhen set to `true`, the Sage agent is added to the agent list and\nthe `:sage` app command is enabled. Defaults to `false`.",
+      "type": "boolean",
+      "default": false
+    },
     "restricted": {
       "description": "Whether restricted mode is active; when enabled, tool execution requires\nexplicit permission grants.",
       "type": "boolean",